application of alternative food-preservation - Bentham Science

162 Application of Alternative Food-Preservation Technologies Bevilacqua and Sinigaglia
On the other hand, mechanistic models are derived from basic principles and are designed to describe
fundamental biochemical or thermodynamic phenomena. If the original model is sufficiently sophisticated, it can
be extrapolated for other situations. They have fewer parameters than the empirical equations and the parameters
have a biological meaning.
As regards model level, models can be conceived as having three levels (primary, secondary and tertiary
models).
A primary model is a mathematical equation that describes the changes of microbial population with the time
(e.g. cell numbers vs time) and results in the evaluation of some fitting parameters (lag time, maximal growth
rate, maximal cell number in the stationary phase, D-value), related with microbial growth/death into the system.
Examples of primary models are the Gompertz, Baranyi and Weibull equations.
A second-level model is an equation describing how the parameters, evaluated through a primary model, change
with changes of environmental or other factors, for examples temperature, pH, aw, preservatives.
In the tertiary-level models, this process is reversed to obtain a prediction concerning a particular pathogen or
spoiling microorganism in a defined system. The tertiary models are usually incorporated into predictive
softwares (ComBase, SSP, Simprevius), that give a good estimation of growth/survival of pathogens and/or
spoiling microflora for different purposes (implementation of the HACCP system and risk assessment).
A crucial question is: why predictive microbiology? which uses?
As reported by Legan [7], PM is an useful tool, able to meet different issues, i.e.:
Establishing safe shelf life for a food product;
Exploring the effects of formulation changes on shelf life (e.g. the addition of an antimicrobial
compound);
Establishing process lethality and optimizing process parameters;
Establishing the probability of pathogen survival in a food and the risk of product failure;
Understanding the behaviour of occurring microflora in a system.
CHALLENGE TESTS
Microbiological challenge tests (MCT) are useful tools to determine if a food can support the growth of spoiling
and/or pathogenic microorganisms; they play a fundamental role in the definition of the effectiveness and/or
lethality of a preserving treatment (e.g. thermal treatments, alternative approaches, addition of antimicrobials).
Moreover, MCT are also useful for the determination of the shelf life of some foods: in this case they can be
labeled as durability test.
Vestergaard [8] reported that there are some crucial factors to be considered when conducting a MCT, i.e.:
1. the selection of appropriate target microorganism, taking into account food composition and
storage conditions;
2. the level of inoculum;
3. inoculum preparation and method of inoculation;
4. duration of the study;
5. sample analysis.
Hereby, we report briefly some details for each factor.
Target Microorganisms
Knowledge of food composition, along with its technological history, is a fundamental prerequisite for the
choice of the target of a MCT; Table 1 reports the microbial targets suggested by Vestergaard for some products.